In the course of servicing or testing components of a fiber optic telecommunication system, such as identifying broken or disrupted optical fiber strands, or identifying active fibers of a fiber optic bundle that are to be connected to an opto-electronic receiver, it is often necessary for a craftsperson to determine whether one or more optical fibers of a fiber optic cable is `dark` or `lit`, namely whether a fiber of interest is conducting light. Since light sources used for lightwave transmission may generate harmful laser radiation, and typically generate an output spectrum that falls within the infrared region (e.g., 780 nm through 1600 nm) that cannot be seen by the human eye, safety precautions must be taken, usually requiring special equipment.
For this purpose, technicians have conventionally used optical power meters to determine the presence or absence of light within a fiber. Unfortunately, optical power meters require that a fiber optic connector be installed on the end of the fiber to be checked. If such a connector is not installed, the craftsperson has nothing more than a bare fiber optic strand with which to work. Unless the end of the fiber is cleaved, light escaping the fiber may be skewed and may not be directed to the detector. As a consequence, before the fiber can be checked for the presence or absence of light, it must be fitted with an adapter to shield the optical detector from the incidence of ambient light (which contains infrared radiation). This procedure is time consuming and involves expensive equipment--the cost for a typical power meter and bare fiber adapter may be on the order of $600 or more.